Italy Responds to Equine Dourine Outbreak

Dourine is a sexually transmitted parasitic disease of equidae, caused by the flagellate protozoan Trypanosoma equiperdum. Recent phylogenetic (the evolutionary relation among groups of organisms) investigations suggest that T. equiperdum and Trypanosoma evansi, the agent of surra, are subspecies of Trypanosoma brucei, transmitted by tsetse flies and widespread throughout Africa. Dourine is endemic in many areas of Asia, Africa, Russia, parts of the Middle East, South America, and southeastern Europe. In Italy, it was originally eradicated in the 1940s, but in the 1970s a serious epidemic occurred.

Dourine is the only trypanosomiasis transmitted solely by the venereal route. The pathogenicity of different T. equiperdum strains is variable.

The diagnosis of dourine can be difficult, as clinical signs and lesions may be absent. Direct diagnosis can also be problematic, given the low number of parasites normally present in infected tissues and the mild, short-lasting parasitemia (parasites in the blood). Additionally, there is serological cross-reactivity with other trypanosomes.

Table 1

In May 2011, a stallion undergoing routine testing in Italy for stud purposes tested positive for dourine in the complement fixation test. The ensuing epidemiological investigation revealed four other outbreaks epidemiologically linked with the first (Table 1).

A nationwide serological survey of all officially recognized stallions and females of reproductive age (> 2 years) ordered by the national veterinary authority revealed two new outbreaks in the regions of Campania and Puglia.

Two stallions and four mares exhibiting clinical signs from different outbreaks were transferred to the Istituto G. Caporale in Teramo in order to study the pathogenesis of the disease and to carry out further diagnostic evaluation. The main signs observed in these horses were rapid weight loss; labial ptosis (drooping); swollen joints; urticarial, plaque-like skin lesions; ventral edema including the scrotum; evidence of lymphatic stagnation; and congestion of the genital mucosa.

Tissues were harvested and tested by a specific real-time PCR assay for the Trypanozoon subgenus. The following samples were positive (in some cases also on direct microscopic examination): mammary tissue, secretions and draining lymph nodes, plaque-like skin lesions, popliteal lymph nodes, cerebrospinal fluid, clitoral groove smear, urine and tear secretion, and intra-articular fluid. T. equiperdum was isolated from the mammary secretion of a naturally infected mare inoculated in the scrotum of a male rabbit.

The distribution of the premises involved, prevalence on the premises and in the surrounding area, and the animals that tested positive (all adult animals used for reproduction) do not correlate with a disease transmitted mechanically by insects like surra. On the contrary, these factors are congruent with a disease transmitted by coitus, like dourine. Also, five of the seven outbreaks were linked by the movement of breeding animals. To date, healthy horses living in contact with symptomatic and parasitemic horses during periods when vectors of T. evansi are likely to have been active have neither developed antibody nor signs of surra.

Currently in progress are studies of the pathogenesis of dourine; molecular characterization of the strain isolated; comparative serologic testing including Western blot, ELISA, and immunohistochemistry; and attempts at in vitro cultivation of the T. equiperdum isolate and its transmission in vivo.

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